Mammals, including humans, lacking pigment in the retinal pigment epithelial cells have a number of abnormalities of the retina and visual system. Similar abnormalities occur in albinos that lack pigment in the entire body including the eye and in ocular albinos that lack pigment only in the eye. We propose that the lack of pigment affects cell proliferation early in the development of the neural retina and that these abnormalities in cell proliferation affect both cell number and cell class in the adult retina. We describe a hypothetical set of behaviors for the proliferating cells of the retina in pigmented vs non-pigmented eyes and then propose specific experiments to test this hypothesis. For this project mice with two different types of non-pigmented retinas will be used: C57BL/6J-tyrc2J/tyrc2J, which are albino, and Oa1tm1Inc/Y which are ocular albinos. These mice have mutations at different locations in the pigment processing pathway, and both have phenotypes that are substantially similar to their human counterparts. The Oa1tmInc mouse is a murine homolog of human Oa1 (also known as Nettleship-Falls Type Ocular Albinism). The pigmented mice that we will use are chosen to have the same genetic background as the non-pigmented mice. The project has 3 specific aims which will examine at high spatial and temporal resolution: 1) the cell cycle, 2) the proportion of daughter cells leaving vs remaining in the cell cycle, and 3) the generation of cells of specific retinal classes. We will achieve both high spatial and temporal resolution for this project using methods developed in this laboratory that exploit double labeling with two S-phase markers, bromodeoxyuridine and tritiated thymidine. The results obtained will tell us the earliest differences in the production of cells in the developing retina for pigmented and non-pigmented animals including information about regional differences within the retina. Such detailed information is important for understanding how the lack of retinal pigment produces abnormalities and for the rationale development of treatments and therapies.